Positive Effects of Climate Change

According to a report in National Geographic News in November 2002, as greenhouse gas levels climb higher in the atmosphere, crop yields may increase in certain areas, such as fruits, vegetables, seeds, and grains. Although this may initially sound like a good thing, the positive effect is short-lived because it also results in a decrease in the crop's nutritional value.

Peter S. Curtis, an ecologist at Ohio State University, says, "But there's a trade-off between quantity and quality. While crops may be more productive, the resulting produce will be of lower nutritional value."

Robert Mendelsohn, an environmental economist at Yale University, says, "There is no doubt but that quality matters. If scientists can demonstrate a distinct loss of quality, this would be important and could change our impression of the global impact of climate change on agriculture from benign to harmful."

In the study conducted by Peter S. Curtis and his colleagues, they relied on data collected from 159 studies over the past 20 years involving 79 different plant species. Each plant had been subjected to twice the normal levels of CO2—an amount equal to what is predicted the Earth's atmosphere will contain by 2100. The collective sampling included a diverse number of species such as corn, wheat, rice, blueberries, cranberries, cotton, pasture grasses, and several versions of wild plants.

One of the key concepts Curtis wanted to focus on was the overall reproductive traits of plants such as the number of seeds and fruit, their size, and their nutritional quality because researchers had already confirmed that increasing CO2 levels did increase the growth of the plant's leaves, stems, and roots.

Curtis stressed the importance of this because the "reproductive traits are key characteristics for predicting the response of communities and ecosystems to global change." In other words, if plants could grow faster but not successfully reproduce, the point was moot.

The results of the study showed that with a doubling of CO2, total seed weight increased 25 percent, the number of flowers increased 19 percent, individual seed weight increased 4 percent, and the number of seeds increased 16 percent. The study did have some unexpected results, however. According to Curtis, "The surprise is that nitrogen levels actually go down with elevated CO2 levels, which reduces the nutritional value of these foods because it lowers the protein content. In some cases, nitrogen levels were 15 to 20 percent lower."

Irakli Loladze, an ecologist at Princeton University, says, "The increase in crop productivity does not make up for the fall in nutritional value of the crops—plants today provide 84 percent of the calories people eat worldwide and are also the source of major essential nutrients." He also noticed that levels of micronutrients (such as iron, zinc, and iodine) also dropped as CO2 levels rose.

Another discovery was that not all crops experienced the same type of growth. Roughly 30 percent had a notable increase in growth—most of these were traditional crops. Wild species, however, used much of their growth energy to produce chemical deterrents and thicker, tougher leaves for protection.

Peter Curtis explained the result: "Six thousand to 10,000 years of breeding have caused domestic plants to put all their energy into seeds and fruits. This leaves them very poorly equipped to deal with the vagaries of nature. But that's okay because we protect them from insects, browsing animals, and disease. Wild plants do not have this luxury."

As CO2 levels increase, researchers are not sure at this time how the wild plant species will be affected—some will be able to adapt better than others. According to Curtis: "Concerning global warming and this dilemma, there will be winners and losers. We may end up with a bunch of fast growing weedy species."

A study conducted by Ramakrishna Nemani at the University of Montana marked the first vegetation inventory and the effects of global warming as it relates to temperature and precipitation from a global perspective. The study, conducted June 2003, showed that global vegetation had increased 6 percent from 1982 to 1999. In the Amazon region, Nemani says a major cause of vegetation growth is due to less cloud cover, resulting in increased solar radiation. The Amazon region accounts for 42 percent of the global increase.

The atmospheric scientist Dave Schimel, who works at the National Center for Atmospheric Research in Boulder, Colorado, keyed in on the impacts due to absence of cloud cover and its significance for increased vegetation. According to Schimel, "Most studies of the effects of climate change have addressed temperature effects, some have also addressed water effects. But some of the most robust observed changes in climate have been in cloudiness and almost no studies have examined trends in solar radiation. So this is a really interesting new perspective."

The increased vegetation growth has been attributed to different causes in different portions of the world. In the Amazon, the cause has been increased sunlight along with no decrease in rainfall. In areas such as Australia, southern Africa, and India, wetter weather trends over the past few decades are attributed to increased rainfall, such as that received during the monsoon periods.

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